Stilbene derivatives by desulfonation

ABSTRACT

The invention relates to novel sulfone compounds of formula I ##STR1## wherein R 1  is an unsubstituted or substituted phenyl or naphthyl radical, 
     R 2  is hydrogen or the radical of the formula ##STR2## R 3  and R 4  are --CN or --COOR 5 , in which R 5  is C 1  -C 4  alkyl, with the proviso that, if R 2  is the radical of the formula ##STR3##  R 3  and R 4  in formula I may be identical or different. The compounds of the invention are valuable intermediates for the preparation of fluorescent whitening agents of the stilbene series.

This is a divisional of application Ser. No. 827,117 filed on Feb. 7, 1986, now U.S. Pat. No. 4,780,558.

The invention relates to novel sulfone compounds, to a process for the preparation thereof, to the use thereof as intermediates for the preparation of fluorescent whitening agents, and to novel asymmetrically substituted stilbene compounds.

The novel sulfone compounds are of formula I ##STR4## wherein

R₁ is an unsubstituted or substituted phenyl or naphthyl radical,

R₂ is hydrogen or the radical of the formula ##STR5##

R₃ and R₄ are --CN or --COOR₅, in which R₅ is C₁ -C₄ alkyl, with the proviso that, if R₂ is the radical of the formula ##STR6## then R₃ and R₄ in formula I may be identical or different.

If R₁ is a substituted phenyl or naphthyl radical, then substituents are for example: halogen such as fluorine, chlorine or bromine;

C₁ -C₄ alkyl (branched and unbranched) such as methyl, ethyl, n-propyl and isopropyl; as well as NO₂ and phenyl.

In the preferred compounds of formula I, R₁ is an unsubstituted or substituted phenyl radical, in particular a phenyl radical which is substituted by C₁ -C₄ alkyl, preferably methyl.

In the preferred compounds, R₂ is the radical of the formula ##STR7## R₄ as a --COOR₅ group is preferably one of the following groups: --COOCH₃, --COOC₂ H₅, --COOC₃ H₇ (n) and --COOC₄ H₉ (n). In preferred compounds, R₄ is --CN.

If R₂ is the grouping ##STR8## Then the two substituents R₃ and R₄ according to formula I, within the scope of the definition, may be identical (e.g. each of R₃ and R₄ is --CN) or different (e.g. R₃ is --CN and R₄ is the --COOR₅ group).

The novel sulfone compounds of formula I, wherein R₂ is the group of the formula ##STR9## are in particular valuable intermediates for obtaining flourescent whitening agents of the stilbene series. Those compounds of formula I, wherein R₂ is hydrogen, are used in particular for the preparation of compounds of formula I, wherein R₂ is the group of the formula ##STR10##

The sulfone compounds of formula I are prepared e.g. by reacting a cinnamic acid derivative of formula II ##STR11## Wherein R₃ is as defined above, with the sodium salt of the benzenesulfinic or naphthalenesulfinic acid of the formula R₁ -SO₂ Na (III) in organic, preferably alkaline, medium to give a compound of formula Ia ##STR12## and, if desired, allowing said compound of formula Ia to react with one further mole of an identical or different cinnamic acid derivative of formula IV ##STR13##

The reaction of the cinnamic acid derivative of formula II with the compound of formula III is carried out in organic medium, e.g. in dimethylformamide, dimethyl sulfoxide or tetrahydrofuran, preferably in alcoholic medium under heat. Suitable alcohols are for example: methanol, ethanol, propanol, isopropanol, butanols, glycols and glycol ethers.

The compounds of formulae II, III and IV are known and can be obtained in known manner. Examples of suitable cinnamic acid derivatives of formula II or IV are:

4-bromomethylcinnamonitrile,

4-chloromethylcinnamonitrile,

methyl 4-bromomethylcinnamate, and

ethyl 4-bromomethylcinnamate.

Examples of starting compounds of formula III are:

benzenesulfinic acid (Na salt),

4-methylbenzenesulfinic acid (Na salt),

4-chlorobenzenesulfinic acid (Na salt), and

β-naphthylsulfinic acid (Na salt).

Compounds of formula I wherein R₂ is hydrogen (formula Ia) are obtained in this manner. Said compounds are used for preparing compounds of formula I, wherein R₂ is the group of the formula ##STR14## by reacting the compounds of formula Ia with one further mole of a cinnamic acid derivative of formula IV. This reaction is carried out with the aid of a base (e.g. NaOH) in an organic solvent. It is preferred to use those solvents which are suitable for a phase transfer reaction, e.g. methylene chloride or chlorobenzene; mixtures of such solvents e.g. with dimethylformamide or dimethyl sulfoxide may also be used. If necessary, the reacton is carried out under phase transfer conditions (with the aid of a phase transfer catalyst such as tetrabutylammonium bromide, butyltriethylammonium bromide or chloride, benzyltributylammonium bromide or chloride).

The novel compounds of formula I, wherein R₂ is the group of the formula ##STR15## are used for the preparation of divinylstilbene compounds including, as novel compounds, the asymmetrically substituted 4,4'-divinylstilbene compounds of the formula ##STR16## wherein R₃ is --COOR₅, in which R₅ is C₁ -C₄ alkyl.

Said stilbene compounds are conveniently obtained by dissolving or suspending the above compounds of formula I, wherein R₂ is the group of the formula ##STR17## in water or in an organic solvent (e.g. lower alcohols such as methanol, ethanol, propanol, isopropanol or butanol, glycols, glycol monoalkyl ethers, polyglycol alkyl ethers, pyridine, N-methylpyrridone, aromatic hydrocarbons and, in particular, dimethylformamide or dimethyl sulfoxide) or a mixture thereof, adding a base to the resultant solution or suspension and heating to a temperature in the range from about 40° to 150° C.

Suitable bases are both inorganic and organic bases such as alkalis, alcoholates or amines, e.g. NaOH, Na₂ CO₃, KOH, K₂ CO₃, LiOH, CaCO₃, triethylamine and pyridine.

The stilbene compounds prepared from the novel sulfone compounds are suitable fluorescent whitening agents for polyester fibres.

The invention is illustrated in more detail by the following non-limitative Examples.

EXAMPLE 1

44.4 g of 4-bromomethylcinnamonitrile together with 36.11 g of the sodium salt of benzenesulfinic acid and 350 ml of ethanol are boiled for 31/2 hours. The product, which precipitates after the mixture has cooled to room temperature, is isolated by filtration, washed with ethanol and then with water and dried in vacuo at 80° C., affording 52 g of the product of the formula ##STR18## with a melting point of 181°-182° C.

By following the same procedure but using 35.53 g of 4-chloromethylcinnamonitrile (melting point: 85°-86° C.) in place of 44.4 g of 4-bromomethylcinnamonitrile, 4-cyanovinylbenzylsulfone is obtained in a yield of 87% of theory.

The compounds listed in Table 1 can be prepared by following a procedure analogous to that of Example 1:

                  TABLE 1                                                          ______________________________________                                          ##STR19##                                                                                                Melting point                                       Example   R.sub.1          (°C.)                                        ______________________________________                                                    ##STR20##       179-181°                                     3                                                                                         ##STR21##       218-219°                                     4                                                                                         ##STR22##       219-220°                                     5                                                                                         ##STR23##       193-194°                                     6                                                                                         ##STR24##       187-188°                                     ______________________________________                                    

EXAMPLE 7

38.26 g of methyl 4-bromomethylcinnamate (melting point: 59°-60° C.) together with 27.9 g of the sodium salt of benzenesulfinic acid and 200 ml of ethanol are boiled under reflux for 3 hours. After the mixture has cooled to room temperature, the precipitated product is isolated by filtration, washed with ethanol and then with water and dried, affording 43.4 g (91.6%) of the compound of the formula ##STR25## with a melting point of 162°-163° C.

By following the same procedure but using equivalent amounts of ethyl 4-bromomethylcinnamate (melting point: 45°-47° C.) in place of methyl 5-bromomethylcinnamate, the compound of the formula ##STR26## with a melting point of 137°-138° C. is obtained.

By reacting methyl 4-bromomethylcinnamate with the sodium salt of 4-chlorobenzenesulfinic acid, the compound ##STR27## with a melting point of 227°-228° C. is obtained.

EXAMPLE 8

28.33 g of 4-cyanovinylbenzylphenylsulfone, prepared in accordance with Example 1, and 22.2 g of bromomethylcinnamonitrile are dissolved in a mixture of 200 ml of methylene chloride and 40 ml of dimethyl sulfoxide. After the addition of 2 g of tetrabutylammonium bromide and 14 g of a 30% aqueous solution of NaOH, the mixture is heated, with fast stirring, to reflux temperature and then held at boiling point for 12 hours. After 5 hours, a further 0.5 g of tetrabutylammonium bromide is added to the reaction mixture. When the reaction is complete, the methylene chloride is distilled off in vacuo, and 200 ml of water are added to the residue. The product obtained is isolated by filtration, finely ground with water, once more isolated by filtration, washed with water and then with ethanol and dried in vacuo at 80° C., affording 42.1 g (97.1% of theory) of the product of the formula ##STR28## with a melting point of 200°-202° C.

The compounds listed in Table 2 can be prepared by following a procedure analogous to that of Example 8:

                  TABLE 2                                                          ______________________________________                                          ##STR29##                                                                     Example R.sub.3   R.sub.4     Melting point (°C.)                       ______________________________________                                          9      CN        COOCH.sub.3 156-157°                                  10      CN        COOC.sub.2 H.sub.5                                                                         166-168°                                  11      H.sub.3 COOC                                                                             COOCH.sub.3 132-133°                                  12      H.sub.5 C.sub.2 OOC                                                                      COOC.sub.2 H.sub.5                                                                         140-141°                                  13      H.sub.3 COOC                                                                             COOC.sub.2 H.sub.5                                                                         135-136°                                  ______________________________________                                    

EXAMPLE 14

21.22 g of the compound prepared in accordance with Example 8 are suspended in 140 ml of ethylene glycol and, after the addition of 5.18 g of anhydrous potassium carbonate, the suspension is heated, with good stirring, for 4 hours at 100°-105° C. The reaction mixture is then allowed to cool to room temperature, and 6 ml of acetic acid are cautiously added. The resultant mixture is stirred for a further 20 minutes at room temperature and then filtered. The filtrate is washed in succession with methanol, water and methanol and dried in vacuo at 80° C., affording 14 g of the stilbene compound of the formula ##STR30## in the form of pale green crystals with a melting point of 222°-225° C.

EXAMPLE 15

27.45 g of the compound prepared in accordance with Example 9 are dissolved in 90 ml of dimethylformamide, and 11 g of a 30% solution of sodium methylate are added to the solution over 30 minutes at room temperature. The mixture is subsequently stirred for a further 30 minutes at room temperature and, in order to complete the reaction, for a further hour at 40°-45° C. After the addition of 10 ml of methanol, the mixture is cooled to 5° C., the precipitated product of the formula ##STR31## is isolated by filtration, washed with methanol and with water and dried in vacuo at 80° C. The yield is 13.7 g of greenish yellow crystals with a melting point of 183°-186° C.

EXAMPLE 16

By employing the compound of Example 10, the following compound is obtained: ##STR32##

Melting point: 151°-153° C. 

What is claimed is:
 1. A process for the preparation of a fluorescent whitening agent of the formula Va ##STR33## wherein R₃ and R₄ are --CN or --COOR₅ in which R₅ is R₁ -R₄ alkyl, which comprises adding an organic or inorganic base to a sulfone compound of the formula I ##STR34## wherein R₁ is an unsubstituted or substituted phenyl or naphthyl radical,R₂ is a radical of the formula ##STR35## and R₃ and R₄ are as defined above, in an aqueous or organic solvent or suspending agent, and removing the aromatic sulfone group by heating to a temperature in the range from 40° to 150° C.
 2. A process according to claim 1 wherein the fluorescent whitening agent is of the formula V ##STR36## wherein R₃ is --CN or --COOR₅, in which R₅ is C₁ -C₄ alkyl.
 3. A process according to claim 2, wherein R₃ is --COOR₅. 